In recent years, lithium secondary batteries are widely used as a power source for electronic equipment such as portable communication equipment and a notebook-sized personal computer. In addition, requests for resource saving and energy saving are raised for international protection of the earth environment, and the lithium secondary battery is being developed as an engine driving or motor driving battery for an electric vehicle, or a hybrid electric vehicle, (hereinafter also to be referred to as “selectric vehicle, etc.”).
Conventionally, a lithium secondary battery is sealed by bonding a tip portion of a battery case containing an electrode body inside with an outer periphery portion of an electrode cap, and this bonding is formed by a method of caulking and/or welding. This battery is caulked (reference should be made to Japanese Patent Laid-Open No. 9-92241 etc.) so that, as shown in FIG. 2 and FIG. 5, a diameter Rbody of a body part of a battery case 16 as well as a diameter Rtop of a caulked portion thereof have the same size.
However, as shown in FIG. 2, when the diameter Rbody of the body part of the battery case 16 as well as the diameter Rtop of a caulked portion thereof are formed to have the same size with a packing 23 provided between the battery case 16 and the electrode cap, pressure is not applied to the packing 23 equally, a gap is created between the battery case 16 and the electrode cap, this gap functions as a path for an electrolyte solution, and through this path, the electrolyte solution existing in the body part of the battery case will leak, which gives rise to a problem.
In addition, as shown in FIG. 5, when the tip portion of the battery case 16 is joined with the outer periphery portion of the electrode cap by welding, and the diameter Rbody of the body part of the battery case 16 and the diameter Rtop of the caulked portion are formed to have the same size, adhesiveness of the battery case 16 and the outer periphery portion of the electrode cap 15A themselves are weak and the joining force thereof will be given only by welding. The battery formed by this method will not give rise to any problem in the case where it is used as a power source for electronic equipment such as communication apparatuses or computers, but it requires sufficient durability against vibrations taking place at the time of starting an engine or at the time of running the engine in the case where it is used as an engine driving or motor driving battery for an electric vehicle, etc., giving rise to a problem that it is difficult to hold long term sealing.
In addition, conventionally, a lithium secondary battery is produced by a manufacturing method in which, at first, an electrode body is inserted into a battery case and disposed at a stable position, the body part of the battery case is narrowed so that the gap between the battery case and the electrode body almost disappears, thereafter, an electrolyte solution is injected into the battery case, subsequently, an electrode cap is mounted at the opening part of the battery case, and the battery case and the outer periphery portion of the electrode cap are joined by squeezing and caulking to seal the battery (reference should be made to Japanese Patent Laid-Open No. 10-27584 etc.).
However, in the manufacturing method described in Japanese Patent Laid-Open No. 10-27584, the electrode body is impregnated with electrolyte solution and thereafter the battery case and the outer periphery portion of the electrode cap are joined by squeezing as well as caulking to seal the battery, and thereby the method has a problem that the electrolyte solution is lifted to the opening part from the body part of the battery case at the time when the battery case undergoes squeezing, the electrolyte solution enters the caulked portion, this electrolyte solution which enters forms a path in the caulked portion, and through this path the electrolyte solution existing in the body part of the battery case would leak.
The present invention has been achieved in view of such conventional problems, and an objective thereof is to provide a lithium secondary battery in which improvement in long period stability as well as reliability has been planned by intensifying the caulking between the battery case and the electrode cap and by removing the caulked gap between the battery case and the electrode cap so as to suppress leakage of the electrolyte solution.
In addition, another objective is to provide a lithium secondary battery in which improvement in long period stability as well as reliability has been planned by intensifying caulking between the battery case and the electrode cap and by welding the tip portion of the battery case with the outer periphery portion of the electrode cap so as to suppress leakage of the electrolyte solution.
In addition, still another objective is to provide a manufacturing method of the above-described lithium secondary battery in which manufacturing is simplified and improvement in productivity has been planned by making complicated operations such as joining operations, etc., inside the narrow battery case unnecessary and by using only selected good battery elements for the subsequent steps.